The weak form developed from 15c. In late Old English also of the arms. Intransitive sense, "become folded" is from c.1300 (of the body or limbs); earlier "give way, fail" (mid-13c.). Sense of "to yield to pressure" is from late 14c. Related: Folded; folding.

n.1

"pen or enclosure for sheep or other domestic animals," Old English falæd, falud "stall, stable, cattle-pen," a general Germanic word (cf. East Frisian folt "enclosure, dunghill," Dutch vaalt "dunghill," Danish fold "pen for sheep"), of uncertain origin. Figurative use by mid-14c.

-fold

multiplicative suffix, from Old English -feald, related to Old Norse -faldr; German -falt; Gothic falþs; Greek -paltos, -plos; Latin -plus, and to fold (v.). Crowded out in English by Latinate double, triple, etc., but still in manifold, hundredfold, etc.